Usually this means you've got something wrong with the data source that the report is connected to. Either you hadn't deployed the data source with the report or it was pointing to the wrong place (e.g. still to development when on live server) or it was in the wrong place ( difference between the default \Data Sources folder and \DataSources for example.) Or the username and password in the datasource is wrong. Redeploying often fixes it by deploying the report and its matching data source.

You can use report manager (usually http://servername[/i%5D/reports) to look at the data source associated with a report by looking at the report properties tab to find exactly which data source is being used (never assume anything!) and then go to that location and data source and check it points to the correct server and database and that the login and password is correct - redo the password for a SQL login.

The incorrect syntax error sounds like something wrong with the stored proc your report is calling. Make sure it works in Management Studio first.